The present invention relates to plasma generators, and more particularly, to a method and apparatus for generating a plasma to sputter deposit a layer of material or to etch a layer of material in the fabrication of semiconductor devices.
Radio frequency (RF) generated plasmas have become convenient sources of energetic ions and activated atoms which can be employed in a variety of semiconductor device fabrication processes including surface treatments, depositions, and etching processes. For example, to deposit materials onto a semiconductor wafer, substrate, or other workpiece using a sputter deposition process, a plasma is produced in the vicinity of a sputter target material which is negatively biased. Ions created within the plasma impact the surface of the target to dislodge, i.e., xe2x80x9csputterxe2x80x9d material from the target. The sputtered materials are then transported and deposited on the surface of the semiconductor wafer.
Sputtered material has a tendency to travel in paths from the target to the substrate, being deposited at angles which are oblique to the surface of the substrate. As a consequence, materials deposited in etched trenches and holes of semiconductor devices having trenches or holes with a high depth to width aspect ratio, can bridge over causing undesirable cavities in the deposition layer. To prevent such cavities, the sputtered material can be redirected into substantially vertical paths between the target and the substrate by negatively charging the substrate or substrate support if the sputtered material is sufficiently ionized by the plasma. However, material sputtered in a low density plasma often has an ionization degree of less than 1% which may be insufficient to avoid the formation of an excessive number of cavities. Accordingly, in some applications, it is desirable to increase the ionization rate of the sputtered material in order to decrease the formation degree of unwanted cavities in the deposition layer.
One technique for increasing the ionization rate is to inductively couple RF energy from a coil to a plasma between the target and the workpiece. Although ionizing the deposition material facilitates deposition of material into high aspect ratio channels and vias, many sputtered contact metals have a tendency to deposit more thickly in the center of the wafer as compared to the edges. This xe2x80x9ccenter thickxe2x80x9d deposition profile is undesirable in many applications where a uniform deposition thickness is needed.
As described in U.S. Pat. No. 6,368,469, issued Apr. 9, 2002 and assigned to the assignee of the present application, it has been recognized that the coil itself may provide a source of sputtered material to supplement the deposition material sputtered from the primary target of the chamber. Application of an RF signal to the coil can cause the coil to develop a negative bias which will attract positive ions which can impact the coil causing material to be sputtered from the coil. Because the material sputtered from the coil tends to deposit more thickly at the periphery of the wafer, the center thick tendency for material sputtered from the primary target can be compensated by the edge thick tendency for material sputtered from the coil. As a result, uniformity can be improved.
As set forth in U.S. Pat. No. 6,652,717, issued Nov. 25, 2003 and assigned to the assignee of the present application, it has been recognized that the sputtering rate for material sputtered from the coil may be nonuniform around the perimeter of the coil. Hence the ability to achieve a desired level of uniformity may be adversely affected in some applications.
It has further been recognized that the coil can develop a hot spot which can cause uneven heating of the substrate. This uneven heating of the coil can also cause reliability problems in that portions of the coil may become too hot and deform, and may also cause particulates deposited on the coil to flake off and contaminate the substrate. Since single turn coils are typically required to carry a relatively high level of current, these problems can be more pronounced in such single turn coils.
In accordance with one aspect of the inventions, a first partial-turn coil and a second partial-turn coil are each provided within a chamber and positioned to couple energy into a central plasma generation area to generate a plasma. In addition, each coil can be adapted to sputter deposit coil material onto a substrate. In one illustrated embodiment, each partial turn coil is a half-turn coil such that the two half-turn coils may be used together to effectively surround the plasma generation area. Such an arrangement is believed to reduce the applied RF voltage across each partial-turn coil such that uniformity may be improved.
In one embodiment, the chamber has a closed ring conductive member to which an RF generator is coupled so as to define two or more partial-turn coils. In another embodiment, separate arcuate-shaped conductive members are coupled to one or more RF generators to provide separate partial-turn coils. To increase the efficiency of the generated RF electromagnetic fields, the generator or generators may be coupled to the partial turn coils in a manner which facilitates coherent currents flowing in the separate partial-turn coils.
There are additional aspects to the present inventions as discussed below. It should therefore be understood that the preceding is merely a brief summary of one or more embodiments of the present inventions. It should further be understood that numerous changes to the disclosed embodiments could be made without departing from the spirit or scope of the inventions. The preceding summary, therefore, is not meant to limit the scope of the inventions. Rather, the scope of the inventions is to be determined only by the appended claims and their equivalents.